Most computer processing is performed by electronics provided on printed circuit boards (PCB) which are mounted on the inside of a chassis. In particular, substantially all personal computers provide a main PCB containing the electronics (e.g., integrated circuits (ICs)) used to carry out the computer's general processing functions. This PCB is often referred to as the "mother board." When upgraded electronics for data processing becomes available for a particular data processing system or if additional memory or processing is desired, an expansion board often referred to as a "daughter board" may be connected to the mother board. As shown in FIG. 1, it is common to provide a mother board 6 which serves as a backplane for mounting additional boards so that the additional boards are electrically interconnected to the mother board. Typically, right angle connectors 7 and 8 have been used to interconnect the expansion boards 4 orthogonally to the mother board 6 via connectors 9 and 10, respectively, as shown by the dash-and-dot lines in FIG. 1.
With respect to the Cartesian coordinate system x, y, z shown in FIG. 1, the expansion boards 4 are positioned with their plane parallel to the y-z plane and are offset mutually in the x direction. The mother board 6 is arranged in parallel to the x-z plane.
For years, the electronics industry, driven in particular by the data processing market, has strived to reduce the size, cost and complexity of data processing components. To reduce the overall size of the chassis housing the PCBs in a data processing system it is desirable to stack the PCBs in parallel rather than in the orthogonal arrangement shown in FIG. 1. Connection assemblies for interconnecting PCBs in a stacked configuration are disclosed in U.S. Pat. No. 5,176,526, Jan. 5, 1993, issued to Hillbish et al. and entitled, "Shielded Stacking Electrical Connector Assembly."
Typically, some of the electrical components on the PCBs are shielded to reduce electromagnetic interference (EMI) caused by other electrical components. For instance, U.S. Pat. No. 5,014,160, May 7, 1991, issued to McCoy and entitled, "EMI/RFI Shielding Method and Apparatus," discloses an apparatus for shielding only selected portions of a printed circuit board. However, it has not been practical or feasible to shield the entire PCB. Therefore, the chassis housing the mother board and expansion boards has provided some shielding on its inner surface to prevent effects from externally generated EMI. Unfortunately, the chassis and partial PCB shielding cannot reduce the EMI effects on a board-by-board basis without shielding each PCB separately.
The high-speed electronics typically associated with expansion boards generate substantial thermal energy. Excess heat, however, may damage the electronic components and generally cause the data-processing system to fail. For this reason, chassis are often enlarged to allow thermal energy to dissipate or to permit installation of an internal fan to cool the electronics. In applications where it is desired to shield the electronics on an individual PCB, it is often necessary to design a cooling system for the PCB. The stacked PCB configuration described above increases the necessity for cooling since the thermal energy generated may be confined between adjacent PCBs.
One solution to the cooling problem has been to design metal heat sinks into the shielding and use a fan to assist in dissipating thermal energy away from the electronics through the heat sinks into the chassis. However, metal heat sinks are relatively heavy and expensive. Moreover, since an internal fan is required, the size of the chassis cannot be reduced.
Another solution introduced by Aavid Engineering, Inc. is to provide a liquid coolant such as Fluronert into a plastic case disposed on top of the ICs. According to this technique, the liquid coolant is heated to boiling by the thermal energy generated by the ICs. A series of tubes leading away from the ICs extend from the plastic case so that the heated coolant in a gaseous state can dissipate and cool. Once cooled, the coolant returns to its liquid state and is recycled back to the plastic case through another series of tubes thereby maintaining the chip at an acceptable temperature. The advantage of this technique is that a fan is not required and, thus, the chassis size may be reduced. However, there are several disadvantages of this technique. For instance, this technique requires custom design for each IC which may also depend upon the configuration of the PCBs inside any given chassis. Thus, its implementation and design are complicated, and its costs, like metal heat sinks, are relatively high.
Pin Gate Array (PGA) connectors are commonly used to connect the expansion boards perpendicularly to the mother board via a zero-insertion-force connectors known as a "ZIFs" or low-insertion-force connectors referred to as "LIFs". However, there are a number of drawbacks associated with interconnecting the expansion boards using PGAs. For instance, the perpendicular orientation shown in FIG. 1 requires the use of an enlarged chassis. Moreover, ZIFs and LIFs are somewhat complicated and relatively expensive. Insertion of an expansion board using PGAs is often difficult because the mother board sockets may not be easily accessible and the pin connectors on the PCB expansion board have no lead-in guidance. Thus, inserting the expansion board using PGAs may require trial and error before the connectors are properly mated. Still further, the PGAs provide substantially no protection for the connector pins. Therefore, the pins may be easily damaged or broken prior to insertion thereby necessitating replacement of the entire expansion board including the electronics.
There is a need for a shielded circuit board connector module and a technique for shielding individual PCBs to be interconnected to a mother board in a stacked configuration. Such shielded modules should provide for adequate heat dissipation and easy insertion and extraction. However, the connector module should allow for a reduction in the size of the chassis as compared to current designs in which an internal chassis fan must be provided. Moreover, the connector module should be simple in design to minimize cost and the complexity of implementation.